by Kentucky Equine Research Staff

Veterinary researchers recently conducted a comprehensive review of 22 studies using platelet-rich plasma (PRP) to treat tendon and ligament injuries in horses.* These soft-tissue injuries are major contributors to lameness and result in substantial economic losses for both owners and trainers. Despite growing interest, limited controlled clinical data support the efficacy of PRP.

PRP is a type of orthobiologic therapy derived from the horse’s own blood. The blood sample is processed, usually by centrifugation, to create a concentrated suspension of live platelets and white blood cells. This mixture is then injected directly into the horse’s injured soft tissue, guided by ultrasound.

“After the PRP is injected, it transforms into a platelet-rich ‘gel’ that releases growth factors and anti-inflammatory mediators,” explained Catherine Whitehouse, M.S., a nutrition advisor for Kentucky Equine Research.

Those molecules then attract nearby stem cells and promote regenerative mechanisms that ultimately help repair and heal damaged tissues.

During the researchers’ review of the studies, they asked six questions that may help owners better understand PRP.

1. Is PRP safe in horses?

Yes, across all 22 studies, no significant adverse effects were reported following PRP treatment.

2. What is the most common way of producing PRP?

Across the 22 studies, fresh whole blood volumes collected from horses ranged from 15 mL to 300 mL, with most researchers using between 50 and 81 mL. The standard method for producing PRP involved a double-centrifugation protocol; however, alternative approaches were used, including single-centrifugation semi-automated kits and gravitational filtration systems.

3. What is the optimal concentration of platelets?

This remains unknown. The platelet concentration in PRP in the studies ranged from 100 x 10³ to 1,370 x 10³ platelets/ìL. When reported (only nine of the 22 studies reported concentration), this value alternated between 1.3 to 8.7 times the concentration of platelets in whole blood.

4. What “dose” of PRP should be injected and how often?

Veterinarians injected platelet-rich plasma directly into the lesions in all studies. The volumes varied dramatically, from 1 mL to 12 mL. Most studies used between 2 mL and 5 mL, and most adjusted based on the size of the lesion on ultrasound. Most studies used a single injection, but one study performed three injections into the same lesions at two-week intervals.

“Considering that the concentration of platelets varied markedly in each PRP preparation, the difference in injected volume further complicates the issue of decoding the optimal dose,” explained Whitehouse.

5. What were the clinical outcomes?

Platelet-rich plasma yielded positive results in 18 of the 22 studies (86%), with researchers citing improvements in lameness, ultrasound appearance, and recovery times. However, researchers only reported positive results in two of the four randomized clinical trials when PRP was used as the only treatment. In the two randomized clinical trials with positive results, lameness scores decreased by 30% to 60% compared to 10% to 25% in the control groups.

The reviewers added, however, “PRP appears to be effective at promoting short- and medium-term recovery, but its long-term efficacy may depend on factors such as injury severity and concurrent therapies.”

6. Can PRP be combined with other therapies?

Yes. All case series and clinical trials included in the review combined PRP with controlled exercise programs to enhance healing.

In some studies, PRP was also paired with mesenchymal stem cells or bone marrow aspirate concentrate. However, current data are insufficient to determine whether these combinations offer added benefit. Further research on combining PRP with other regenerative therapies, such as extracellular vesicles or gene therapy, is needed.

“Standardized reporting and methodological rigor of PRP studies should be improved to ensure reproducibility and facilitate evidence-based veterinary practice,” concluded the researchers.

“To support the horse’s musculoskeletal system, including soft-tissue structures and joints, offer oral joint health supplements,” recommended Whitehouse.

^*Carmona, J.U., and C. López. 2025. Efficacy of platelet-rich plasma in the treatment of equine tendon and ligament injuries: A systematic review of clinical and experimental studies. Veterinary Science 12(4):382.

Reprinted courtesy of Kentucky Equine Research. Kentucky Equine Research is an international equine nutrition, research, and consultation company serving horse owners and the feed industry. Our goals are to advance the industry's knowledge of equine nutrition and exercise physiology, apply that knowledge to produce healthier, more athletic horses, and support the nutritional care of all horses throughout their lives. Learn more at Kentucky Equine Research.

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Editor's Note: This is an important topic for us. We had a horse die from Potomac Horse Fever in New York State even though he was vaccinated, but it is still important to vaccinate your horses and watch for signs of this potentially deadly disease. 

As summer heats up, so does concern over a serious equine illness: Potomac Horse Fever (PHF). Once considered rare in Canada, PHF is now appearing more frequently prompting veterinarians and horse owners to stay alert.

What Is Potomac Horse Fever?

Potomac Horse Fever (PHF), also known as equine neorickettsiosis or equine monocytic ehrlichiosis, is a serious intestinal disease that affects horses, especially during the warmer months. It was first identified in 1979 near the Potomac River in Maryland, but cases have since been reported across North and South America— including a growing number in Canada. PHF is caused by a type of bacteria called Neorickettsia. For many years, the only known culprit was Neorickettsia risticii. However, researchers in Canada and USA have recently discovered a new species, Neorickettsia findlayensis, in horses showing signs of PHF.

These bacteria live inside tiny parasitic flatworms (called trematodes) that infect aquatic insects like mayflies, caddisflies, and dragonflies. Horses can become infected when they accidentally eat these insects—often while grazing or drinking from contaminated water sources. Once inside the horse’s digestive system, the bacteria are released and begin to invade the lining of the colon and cecum. From there, they can enter the bloodstream and infect immune cells, leading to symptoms like fever, diarrhea, and in severe cases, laminitis.

PHF is typically a seasonal disease because the insects that carry the bacteria are most active in summer and early fall.

Why the Sudden Rise?

According to Dr. Luis Arroyo from the Ontario Veterinary College, climate change and shifting insect populations may be contributing to the spread of PHF into new regions, including parts of Ontario where it wasn’t previously seen. Increased awareness and better diagnostic tools are also helping identify more cases.

Signs to Watch For

PHF can come on suddenly and progress quickly. Common symptoms include:

• High fever
• Lethargy
• Loss of appetite
• Diarrhea
• Colic-like symptoms

 

In severe cases, laminitis (a painful hoof condition) or even abortion in pregnant mares Early detection is critical. If your horse shows any of these signs, contact your vet immediately.

Diagnosis and Treatment

Diagnosis typically involves blood and fecal tests, including PCR testing. Treatment usually includes oxytetracycline, an antibiotic that can be effective if given early. Supportive care like IV fluids may also be needed.

Prevention Tips

Talk to your veterinarian to learn about available vaccines and how well they protect against different strains of PHF, including newer ones found in Canada.

Other preventive steps include:

• Turning off barn lights at night to avoid attracting insects
• Covering water troughs and feed bins
• Cleaning up dead insects around the barn
• Avoiding turnout near ponds, rivers or streams during peak insect season

 

PHF is a serious but manageable disease. With vigilance, early intervention, and preventive care, horse owners can help protect their herds.

Resource Links

Potomac Horse Fever (PHF) Webinar

Potomac horse fever in Ontario: Clinical, geographic, and diagnostic aspects.
Arroyo LG, Moore A, Bedford S, Gomez DE, Teymournejad O, Xiong Q, Budachetri K, Bekebrede H, Rikihisa Y, Baird JD.
Can Vet J. 2021 Jun;62(6):622-628. PMID: 34219771; PMCID: PMC8118184.

 

This article originally appeared on Equine Guelph, The University of Guelph and is published here with permission.

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